Tooth pulp afferents are known to project to nucleus caudalis, (in addition to other regions of the trigeminal nucleus), a region believed to play a major role in pain processing of oral-facial stimuli. However, many questions concerning the processing and relay of tooth pulp input within the nucleus still remain unanswered. It is the aim of this project to study (a) the distribution of tooth pulp afferents in nucleus caudalis, (b) the responses of neurons in the nucleus to tooth pulp stimulation and the projection targets of these neurons, (c) the modulation of tooth pulp activated neurons by nucleus raphe magnus, periaqueductal gray and other brainstem regions and determining the pharmacology of these descending influences. The experiments will involve standard electrophysiological recording techniques in anaesthetized cats. The results of this study will help explain the neurophysiological basis of dental pain as well as other pains such as trigeminal neuralgia for which tooth pulp input may share a common path or at least serve as a useful model. These studies may also provide new insights into, and possible improvements of, the recent methods of transcutaneous nerve stimulation and brain stimulation produced analgesia being used to treat some pain conditions.